Breast milk is the ideal infant nutrition source. Extensive research documents the innumerable positive health outcomes and economic benefits of breastfeeding for both mothers and infants. Despite this, women in the United States do not breastfeed for as long as national recommendations. Breastfeeding is a complex process, requiring the successful integration of demographic, psychosocial, and biomedical factors. In the past, environmental chemicals with estrogenic properties have been associated with shortened durations of lactation. This potential barrier to breastfeeding, however, has not been re-examined recently or studied in detail with more than one estrogenic chemical. Although concentrations of environmental chemicals in breast milk may be low, cumulative exposure may be associated with negative lactation effects. The long range goal of this project is to examine the potential for environmental chemical contamination of breast milk to contribute to shortened lactation duration. The objectives of this proposal are to 1) determine potential factors that may impact concentrations of estrogenic environmental chemicals in breast milk, 2) characterize the changes in chemical concentration of estrogenic chemicals in breast milk over the course of lactation, and 3) establish if cumulative concentrations of these chemicals in breast milk are associated with shortened lactation duration. If environmental chemicals are shown to negatively impact breastfeeding duration, the discovery of modifiable factors to reduce breast milk contamination can be pursued. The candidate for this Career Development Award is Sheela Geraghty, MD, MS. Dr. Geraghty is a pediatrician with training in epidemiology, environmental health, and lactation. Dr. Geraghty's overall career goal is to incorporate her skills as a researcher and clinician into a program that will help women increase breastfeeding success and breastfeed longer. The Cincinnati Children's Hospital Medical Center, where Dr. Geraghty is a junior faculty member, has distinctive resources in which to help her successfully achieve this goal, including the Cincinnati Children's Environmental Health Center and the Cincinnati Children's Research Human Milk Bank. The mentors identified in this proposal are experts in the fields of lactation, environmental health, nutrition, physiology, statistical analysis, and clinical breastfeeding management. Identifying barriers to breastfeeding is in the interest of all Americans to improve child and maternal health outcomes.